Integration degrees of integrated circuits have been more and more increasing. As a result, ultrafine pattern processing with subquater-micron line width becomes necessary in producing semiconductor substrates such as very-large-scale integrated circuits. As one of techniques for fine pattern making, it is known to shorten the wavelength of an exposure light source to be used in resist pattern making
In producing semiconductor devices up to 64 Mbit, for example, it has been a practice to employ the i-beam (365 nm) of a high pressure mercury lamp as the light source. As positive resists suitable for this light source, a large number of compositions containing a novolac resin and a naphtoquinone diadize compound as a photosensitive substance which have accomplished satisfactory results in processing at a line width of about 0.3 μm have been developed. In the production of semiconductor devices of 256 Mbit or more in the degree of integration, use has been made of a KrF excimer laser beam (248 nm) as an exposure light source.
To produce semiconductor devices of 1 Gbit or more in the degree of integration, furthermore, attempts have been recently made to use an ArF excimer laser beam (193 nm) and an F2 excimer laser beam (156 nm) for forming patterns of 0.1 μm or less.
The tendency to shorten the light source wavelength as described above brings about large changes in components constituting resist materials and structures of compounds used therein.
As resist compositions for the exposure with the KrF excimer laser beam, so-called chemical amplification resists comprising a resin which has poly(hydroxystyrene) showing small absorption in the 248 nm range as the fundamental skeleton and protected with an acid-decomposable group as the main component together with a compound capable of generating an acid upon far ultraviolet light irradiation (a photo-acid generator) have been developed.
As resist compositions for the exposure with the ArF excimer laser beam (193 nm), chemical amplification resists with the use of an acid-decomposable resin in which an alicyclic structure showing no absorption in the 193 nm range is introduced into the main or side chain of a polymer have been developed.
In the case of using the F2 excimer laser (157 nm), it is clarified that even such an alicyclic resin as described above is insufficient for obtaining a desired pattern of 0.1 μm or less because of showing large absorption in the 157 nm range. It is also found out that resins having a fluorine atom introduced therein (perfluoro structure) have sufficient transparency at 157 nm. Thus, various resist compositions containing fluororesins are discussed in, for example, JP-A-2003-57826, JP-A-2002-333715 and JP-A-2002-341543.
However, these fluororesin-containing resist compositions for F2 excimer laser exposure suffer from the problem of bottom spread.